Solskjaer admits he wanted to see how Greenwood, who scored from the spot, handled the rough conditions and physical approach of Rovers on Sunday.
The manager said, "The first 15-20 minutes might have been a cultural shock for Mason.
"It's a different football than he's used to. He lost the ball and made a good tackle after 20 minutes. After that he played very well.
"It's about trying to give him that responsibility and ownership."
On the penalty, Solskjaer added: "Mason should always want to take penalties. I wanted to give him some responsibility."